Method of making magnetic cores



May 15, 1962- J. J. VIENNEAU ETAL METHOD OF MAKING MAGNETIC CORES Original Filed April 23, 1955 In l e'rzfil' Jacob d P71907764?! Kerzrzefr? D Beards/5y,

United States Patent 3,034,203 METHGD OF G MAGNETKC CGRES Jacob J. Vienneau, Pittsfield, and Kenneth D. Beardsley, Dalton, Mass., assignors to General Electric Company, a corporation of New York Original application Apr. 23, 1953, Ser. No. 350,722, now Patent No. 2,937,352, dated May 17, 31966 Divided and this application Feb. 27, 1958, Ser. No. 713,080

1 Claim. (ill. 29-15557) This invention relates to magnetic cores, and more particularly, to an improved method of making magnetic cores and linking the same with electrical coils.

This application is a division of our patent application Serial No. 350,722, filed April 23, 1953, and now Patent No. 2,937,352.

A known form of butt joint laminated magnetic core structure comprises a continuous and relatively narrow strip of flat thin metallic magnetic material wound continuously into a rectangular or annular core section with a window opening therein. Each of the layers or turns of the magnetic strip material is superimposed and con-- centric with respect to each other.

When used in a transformer apparatus, electrical winddisassembled when the core is hinged open. Also, the

various laminations must be held together so they wont become misaligned from their original uncut positions I so that the butt joint can be'accurately closed.

In the known prior art the holding means employed are rigid means like welding, mechanical clamps, or hardsetting enamels, varnishes, or cements. For instance, prior to cutting, the laminated core section may be impregnated with a hard setting varnish. After the varnish sets it rigidly bonds adjacent laminations'of the core section together.

A disadvantage of hard setting or rigid holding means is that relatively little play or freedom of movement is permitted between adjacent laminations when the core section is hinged or pried open. Asa consequence, when the core section is hinged openjmechanical stresses are formed in the various laminations which cause electrical losses in the magnetic core.

Another problem encountered in the prior art is that during the cutting operation the cut laminations have burrs formed thereon. The burrs of each cut lamination make electrical contact with adjacent laminations. That is, a short circuit is formed in the core at the cut portions. This short circuit condition also causes electrical losses in-the magnetic core.

'Itis an objectof this invention to provide a method of constructing a butt joint strip wound laminated core section wherein adjacent laminations are elastically bond- I 7 ment of bonding the turnstogether with an elastic and dielectric material so as to retain them together while still afiording' them a limited amount of movement to facilitate opening and closing of the core.

Our invention also comprises a method of makinga butt joint strip wound-laminated magnetic core section amazes Ce P e iterated May 15, 1962 comprising impregnating a strip wound laminated core section with an elastic electrical insulating bonding material, applying compressive forces to.-a portion of said core section, cutting said compressed portion to form a butt tration of how a butt joint strip wound laminated core section is pried or hinged open to receive a prewound electrical winding coil assembly to belinked therewith. FlGURE 3 is an enlarged view of a butt joint portion of a laminated core section with clamps applied to said portion. FIGURE 4 is an enlarged view of the ends of the cut laminations of an elastic binder impregnated core section portion while compressive forces are applied to said portion. FIGURE 5 is an enlarged view of the ends of thecut larninations after the compressive forces have been removed.

Referring now to FlGURE 1 of the drawing, there is shown therein a rectangular like strip wound laminated core section 1 having a cut or butt joint 2 so that the core section 1 can be hinged or pried open about a hinge portion 3, as illustrated in FIGURE 2, so that a pre wound electrical winding coil assembly, not shown, can

be linked with the core section 1. A' strap or clamping means 4 aids in holding the core sectionjl closed after the winding coil assembly, not shown, is linked with core section 1. v

The rectangular-like core section 1 is formed by spirally winding a relatively narrow flat thin strip of metallic 'magnetic material into a plurality of superimposed and concentric laminations. Adjacent laminations are spaced a sufiicient distance from each other to permit impreg-v that the core section 1 can be hin'ged open about a diag- 1 on'ally opposite corner 3. After the core section is wound it s annealed before impregnation and cutting to'remove stresses set up in the laminations during the Winding operation. g j

'Prior to formation of the butt joint or cut Zthe core section 1 is impregnated with an elastic dielectric bonding material. The elastic bonding material holds adjacent larninations of core section '1 together so that they wont become disassembled during the opening or hinging oper'ati'onf- By viewingjFlGURES l and Zit will be seen that the outer laminations of the cut core section 1 are longer-than the inner laminations. During the hinging or opening operation the outer and longer laminations require a greater degree of movement or play than the shorter inner ;laminations. If rigidrnean-s are used to hold the various -cut laminations together during the opening operation comparative free and unstressed movement of the longer laminations with respect to the shorter laminations is not permitted. That is, with rigid holding means the various laniinations are buckled and distorted and have mechanical stresses formed therein. cause electrical losses in the magnetic core section.

However, with elastic holding means, limited free and easy movement of the various laminations with respect to each other is permitted during the hinging operation These mechanical stresses s causing a minimum of mechanical stresses when the core section 1 is closed the elastic bonding mate- 7 rial permits and aids the various laminations to assume their .origin'aLuncut positions relative to .each other so that the buttjoint 2 can be accurately closed.

The faces of the butt joint can be painted withthe elastic bonding material to aid in keeping the core section ;closed.. Affurther advantage of having an elastic adhesive hnpregnant as the holding means is that audible noise is {decreased When'a transformer is operating vibrations arejset up in the magnetic core. Elastic substances are good sound dampers. Consequently, by impregnating the core and painting the faces of the butt joint Withan elastic hinder the amount of audible noise is decreased. i

Most impregnating'materials set up a strain in the surface-of the core l-arn'inations due to shrinkage. An'elastic adhesive minimizes this effect.

-:be furtherheld to a minimum by impregnating onlya partof the core, or by a purposely incomplete impregna- ".tion so that the adhesive between a pair of adjacent laminations is present only instreaks,

After impregnation of the core an elastic adhesive v v and setting of the same and prior. to cutting of the core to form a butt joint the portion of the coreto be cut is' subjected to compressive forces. Thus, as seen in FIG- URE}, the corner or portion to be cut is compressed, as

by a pair of clamps comprising horizontal bars 5' joined at opposite ends by threaded bolts 6. .Nuts 7 when threaded down on bolts 6 place the portion'to be cut in compression. .It should be noted that the compressive forces are applied substantially perpendicular or against the flat surfaces or planes of the laminations to be cut.

,These compressive forces compress the layers of elastic fbon'ding material located between the various laminations of the core portion tobe cut. 7

The'purpose of compressing the elastic bonding material in the area to be cut is illustrated 'in FIGURES 4 and v .5. As seenin FIGURE.4, when thecut F2 is made burrs S are formed at the ends of the cut laminations 9 which have compressed elastic bonding material Ill therebe-. tween. The burrs 8 make electrical contact with adjacent laminations; Since all the laminations are then electri- 1 cally interconnected a shortcircuit is formed in the laminated buttjoint coreat the faces of the butt joint. This ,short circuit condition results in'electrical losses in the magnetic core. 1 V

p However, by using an elastic'dielectric bondingrnaterial and. compressing the, bonding material prior to cutting this shortcircuit condition is'uniquely relieved.- 'In FIGURE 5 is shown what occursafter the clamps of [FIGURE 3 are removed after the cuttingoperation- LThe I compressed elastic bonding mate'rial it} expands toits. substantially original-non-compressed state. :Expansion of: the'materialltl causes the cut core laminations 9 to be 5 separated a sufiicicnt distance to take the burrs 8 out of electrical contact with-adjacent laminations 9. Thus, the

short circuit condition of FIGURE4 is removed;

1 It is to be noted that the whole core structure need not V necessarily be impregnated with the elastic 'binder; For.

instance, only a portion of the core at the area to be cut need be impregnated if this partial impregnation of Further,

therein.

Also, these strains can 10 sections which are to be butt jointed together. Accord- I ingly, by the term annular core section we do not intend to restrict ourselves to a circular wound core section having .a Window opening therein, but intend that theterrn com- .p'ris'e any closed core. section having a window opening The elastic impregnant used does not constitute part of this invention but is a substance that can be readily purchased onthe market. It should not be hard setting, but should be elastic to permit limited freedom of move- '20 ment between the various larninai-ions during the'hinged opening operation, and should be adhesive enough to hold the variousflaminations from becoming disassembled. I An elastic adhesive that has given good results is a syn-5 j jitheticth'ermo-setting rubber-base adhesive of the buta- 4 dieneacrylonitrile type. The elastic adhesive selected must not be corroded by transformer insulatingoils.

i ,While there'has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing *r'roml the invention, and that it is intended by the appended claim to cover all such changes "and miodifications as fall within the true spirit and scope of the invention. f

What we claim as new and desire to secure by Letters Patent of the United States is:

A method of making a magnetic core and linking the same With'a'. preformed electrical coil, said method comprising winding and forming a continuous strip of mag netic materialinto a curved core' having radially nested 40' and spaced spiral turn laminations, annealing said curved core, bonding said laminations with respect to each other by impregnating said laminations with an elastic and dielectric bonding material, placing a part .ofzsaid core under compression to compress its bonding material,

cutting, through said compressed 'part to form a core having a single butt jointand single turn cutlaminations relieving. said compression to expand said compressed bonding materialto separate edge burrs on said single turn cut laminations, hinging said curved core open by hinged movementof said; bonded and cut laminations in a direction away from said joint about a, part of said core which is oppo'site to the part of said core having said joint therein, linking said hinged open core with a u preformed electrical coil, and then closing said electrical coillinked core by hinged movementv of said bonded laminations in an opposite direction to close said joint.

References Cited in the file of this patent UNITED STATESPATENTS 2,478,029 Vienneau Aug. 2,1949

- 2,830,277 -Ka'ne i Apr. .8, 1958 

